Cutting and sewing lines are usually marked by pencil, chalk or soap which are manually placed on the material to be worked using a straight edge. However where the material to be worked is flexible or when it is not flat, and particularly when it has compound curves, it is difficult to place the mark with accuracy.
The present invention provides a line of light which illuminates such work pieces, thereby allowing the operator to position a blade, sewing machine needle, etc. at the exactly desired cutting position. If desired, only a single point on the work piece need be marked to establish where the line of light should be placed.
Systems for producing position indicating lights are not new. For example, U.S. Pat. No. 4,799,747 issued Jan. 24th, 1989, invented by Yamakawa, produces a line of light. A light beam emitted by a semi-conductor laser passes through a collimator lens and a cylindrical lens. The emitted light beam is in pencil form, and is deflected into a scanning line by means of a mechanical rotated multi-faceted mirror. The scanning point of light is then focused along an axial plane on the surface of a cylindrical drum.
That system is unsuitable for use in the present invention for the reason that the light beam that enters the cylindrical lens experiences no dispersion. Thus it is suitable at this point to indicate a target point but not a cutting line. Dispersion along a line is provided by scanning using the multi-faceted mirror. The presence of a mechanically rotating structure introduces the possibility of error including thickening of the line. Misalignment of any of the multi-faceted mirrors can occur due to vibration, wear, temperature variations, etc., thus thickening and misplacing the line.
In addition, since the rotating drum in Yamakawa is fixed in position relative to the light source and the optics, in order to have the highest resolution for that structure, the light beam should be focused as narrowly as possible on the surface of the drum. If the Yamakawa structure were to scan a line on the surface of a workpiece which is not planar along the scanning line, the light beam would go out of focus, compounding the errors caused by wear, mirror misalignment and mispositioning, etc. The Yamakawa structure clearly has characteristics which would not allow it to be used in a precision workpiece light marking system.
U.S. Pat. No. 4,693,567 issued Sep. 15th, 1987, invented by Ozaki creates a line of light without mechanically rotating structures as in Yamakawa. This structure utilizes a spherical reflector which intercepts a broad beam created by the divergence of a laser beam. Because of the divergence, as stated in the patent the obtained laser beam has a diameter of a few millimeters to several tens of millimeters. This beam is then reflected by a reflector. Clearly such a broad beam is difficult to position precisely, e.g. to less than one millimeter at a distance of two meters as achieved by systems using the present invention.
The beam in Ozaki appears to be focused on a target. A blank spot would result caused by interception of the beam by the reflector, thus providing a non-illuminated spot. The Ozaki structure thus has limitations in marking a structure having a multi-level surface, and would require refocusing for workpieces placed at or having surfaces at various distances from a saw blade, e.g. 2.5 cm to 2.5 m, which variation can be accommodated in the present invention.
U.S. Pat. No. 4,203 652 issued May 20th, 1980 invented by Hanada utilizes a convex lens and a cylindrical lens for collimating a beam. The focal points in this reference are critically placed in order to collimate the beam. There is no dispersion of the light beam. In order to provide a line of light, a reflector such as described in Osaki or in a mechanical system as in Yamakawa would have to be used.
Light marking systems can thus be produced according to the prior art which produce a spot of light, a cross hair or equivalent, or which require mechanical scanning structures.